Computers frequently feature a visual display unit having a screen upon which information and/or graphics are shown. The screen is most often of the cathode ray tube type but may be a plasma gas display, an electro luminescent flat screen, a liquid crystal display, or another type of display.
It is well known to attach an optical element to a visual display screen or form an optical element as an integral part of such a screen. Magnifying lenses are sometimes used to increase the size of the image created by the visual display unit. Tinting lenses are frequently used to change the color of the light output of a visual display screen, hereinafter referred to as a screen, for the purpose of reducing eye strain. It is also known to place a fine mesh filter over the front of the screen, or apply a coating to the front of the screen, to reduce glare.
It is not possible to change the optical characteristics or function of a prior art screen to suit particular application problems if the lenses and filters are formed as an integral part of the screen or permanently attached to the display unit. With the rapid expansion of the use of microprocessors new applications for visual display units are being developed daily. In many applications more than one user may be required to use a single visual display unit and many different programs may be used on a computer which is limited to a particular screen and lens conbination. The eyesight and preferences of different users may make one type of lens satisfactory for one user and objectionable to another. For example, one user may be confronted with a problem of sunlight being reflected from the screen and causing glare at one particular time of the day while another user using the same display unit at a different time may require magnification of the screen image to compensate for poor eyesight. Prior art display units with integral lenses and filters do not offer any way of subsequently altering the optical characteristics of the screen in such situations.
In recent years the amount of information to be displayed on a screen is being increased with the necessity of reducing the size of characters. This is true in part because most screens have a field only 80 characters wide while most printers have a possible field of 132 characters wide. As manufacturers of display units strive to make characters smaller, the need for magnification of the display is increasing. The new plasma gas displays have exceptionally fine resolution with characters being formed on a screen having thousands of dots per inch. Such a plasma gas display can make characters that are very small.
While it is known to place a magnifying element in front of a television on a stand placed on the floor in front of the television, such a device is inappropriate for use with a computer visual display unit because it would block access to the display unit and would be difficult to adjust to the needs of different users.
Different computer programs may create any number of displays and display formats on a screen. Recent innovations include the advent of a split screen display wherein the screen may be divided into two or more parts. The purpose of such an arrangement is to fit additional data on a screen which may also result in a reduction in the size of the characters displayed on the display unit. In addition, a single magnifying lens attached to or placed in front of a display unit is not well suited for use with a split screen display.
Magnifying lenses, and particularly low cost lenses, typically have a low distortion area in the central part of the lens with increased distortion about the periphery of the lens. Such distortion is objectionable in single cell displays and is even more objectionable in split screen displays since large portions of the display may have to be viewed through a distorted portion of the lens. A single magnifying lens attached to or places in front of a diaplay unit fails to offer any way of adjusting the lens to position the low distortion, or central, part of the lens over a selected part of the screen.
These problems have been overcome by the present invention which realizes other advantages and offers users a choice in optical elements and adjustability in positioning the optical elements that was not previously available.